For many years, ophthalmologists have used keratoprosthetic implants in an attempt to restore vision to patients whose corneas have been injured or become opaque. Their attempts are well documented by patents and other publications. For example, U.S. Pat. Nos. 2,517,523 to Batchelder, 2,714,721 and 3,458,870 to Stone, Jr., 2,754,520 to Crawford, Jr., 2,952,023 and 3,454,966 to Rosen, 3,945,054 to Fedorov et al., and 4,470,159 to Peyman each disclose keratoprosthetic implants. These implants are generally classified by their relationship to the surrounding corneal tissue.
The Stone, Jr., Fedorov et al., and Peyman patents disclose implants designed to be inserted between surgically established corneal layers and anchored in place by the ingrowth of the stroma. Some of these also include removeable lens elements coupled to the anterior chamber supporting means that it anchored between the corneal layers. For a general review of intralamellar keratoprostheses, see Cardona, "Keratoprosthesis", American Journal of Ophthalmology, Vol. 54, 284-294 (1962).
The Rosen patents disclose two-part implants comprising a retaining ring secured to the corneal rim and a transparent plastic member that is secured to the retaining ring.
Crawford, Jr. discloses an implant having upper and lower flanges. After a circular portion of the cornea is removed, the implant is inserted and rotated until the corneal rim is engaged in the recess defined by the flanges.
Each of the above implants, however, has one or more associated drawbacks. The Stone, Jr., Fedorov et al., and Peyman implants require the difficult surgical procedure of surgically establishing corneal layers and thereafter inserting a prosthesis between the layers. The Rosen implants require the surgeon to first attach a retaining ring and thereafter attach a lens to the retaining ring. The Crawford, Jr. implant requires a surgeon to make a first surgical cut to remove a circular piece of the cornea, and a second surgical cut to facilitate introduction of the implant into the circular opening. the surgeon must then delicately position and rotate the implant until it is correctly seated on the corneal rim. Another drawback of many corneal implants is the tendency for the corneal membrane tissue to overgrow the posterior portion of the prosthesis, thereby interfering with light perception and altering light projection.
Alternatively, the damaged cornea can be replaced with a human donor cornea. However, this procedure also has numerous associated drawbacks. The patient can have an adverse reaction to the donor cornea tissue, or the donor cornea itself can deteriorate from aging or ulceration. However, themost common postoperative complication from using donor corneas is the development of corneal astigmatism, i.e., defective vision resulting from a lack of symmetry in the cornea. This is often caused by deformation of the donor cornea from the pull of the sutures used to attach the donor cornea to the patient's cornea. Additionally, there is a chronic shortage of donor corneas.
Thus, there is a continuing need for a corneal implant that (1) can be attached using only simple surgical techniques, (2) can prevent the growth of corneal membrane over the posterior portion of the implant, (3) does not adversely react with the patient's cornea, (4) does not deteriorate from aging or ulceration, (5) prevents astigmatism resulting from deformation caused by the pull of sutures, and (6) is available in an abundant supply.